Mean Value problem

Hi, I was wondering if anyone can help with this problem

Suppose that a tumor grows at the rate of r(t) = kt grams per week for some positive constant k, where t is the number of weeks since the tumor appeared. When, during the second 26 weeks of growth, is the mass of the tumor the same as its average mass during that period?

Suppose that a tumor grows at the rate of r(t) = kt grams per week for some positive constant k, where t is the number of weeks since the tumor appeared. When, during the second 26 weeks of growth, is the mass of the tumor the same as its average mass during that period?